1. Field of the Invention
The present invention relates generally to a semiconductor device and a method of manufacturing the semiconductor device, and particularly to a technique of forming a polysilicon film of which a polysiliccn resistor, an electrode, etc. are made.
2. Description of the Related Art
FIG. 1 shows a structure of a conventional semiconductor device having, for example, a polysilicon resistor.
An insulating film 12 is formed on a semiconductor substrate 11. A polysilicon resistor 13 is formed on the insulating film 12 in a mesa shape. A passivation CVD film 14, for example, is formed on the polysilicon resistor 13.
This semiconductor device is formed by the following method.
First, the insulating film 12 is formed on the semiconductor substrate 11. Then, using a vacuum CVD device, for example, a polysilicon film having a grain size of 0.01 to 0.1 .mu.m is formed over the entire of a major surface of the substrate 11. The polysilicon film is etched by a selective etching process, thereby obtaining the polysilicon resistor 13 having a desired shape. Further, the passivation CVD film 14, for example, is formed over the entire semiconductor structure.
In the semiconductor device thus manufactured, however, the polysilicon resistor 13 has a mesa shape and therefore the surface of the substrate 11 is uneven. Consequently, metal wires formed on the polysilicon resistor 13 may be cut and the reliability of the product may be degraded.
Further, since the polysilicon resistor 13 is composed of granular crystals, the grain size may vary in a heat treatment step of electrically activating impurities in the polysilicon resistor 13 and in a heat treatment step performed after the formation of the polysilicon resistor 13. As a result, the carrier mobility in the polysilicon resistor 13 varies and the uniformity of the polysilicon resistance is deteriorated.
As has been stated above, in the conventional semiconductor device, since the polysilicon resistor is formed on the insulating film in a mesa shape, metal wires formed on the polysilicon resistor may be cut and the reliability of the product may be degraded. In addition, the grain size may vary in a heat treatment after the formation of the polysilicon resistor, and the uniformity of the resistance is deteriorated.